Small cartridges which hold large quantities of carbon dioxide or other gases under compression are well known in the art, for inflating life preservers, vests, rafts, or other similar such devices. Typical ones are shown in the Mackal patents, Nos. 3,809,288; 4,223,805; 4,267,944; 4,498,605; 5,058,635; and 5,333,656. As U.S. Pat. No. 5,333,656 pointed out, one problem in the industry followed from the fact that there existed no real way to quickly determine whether a cartridge attached to an inflator had been used or not. Since a discharged cartridge is virtually identical in outward appearance to a fully charged one, a danger always was present that once a user discharged and repacked the inflatable device, he or she might simply forget to replace the discharged cartridge first with a new one. As this patent noted, the only way to check the status of the cartridge was to unscrew it, and visually inspect its membrane to see whether it had been punctured.
The solution to that problem, in U.S. Pat. No. 5,333,656, was to paint a red sign on an inflator arm, to appear in a window when the arm was in the discharge position, indicating that the cartridge was spent. The theory behind it was that until a full cartridge was placed into position instead, the red sign would not disappear. Testing, however, showed that while that might be what was desired, the red sign often disappeared when one screwed the spent cartridge back in place, or when it was replaced with one that had already been discharged. Further testing revealed, in fact, that no matter what the condition of the replacement cartridge was, the red sign on the inflator arm was moved out of the viewing area--and not necessarily only when a full cartridge was reinserted. Investigation revealed that this followed from the irregular type hole the patent's chisel-shaped pin produced in puncturing the cartridge--so that upon replacement, the frequent misalignment between the pin and the hole which resulted pushed the pin backward, causing the red sign to disappear from the window. The purpose of the invention--to show that an empty cartridge was in place--oftentimes thus was defeated.
Further testing showed that even with the improved puncture pin described in Mackal's earlier U.S. Pat. No. 5,058,635, the problem persisted--and for the reason that the chisel-shaped head often caused the puncture hole rim to snag on the pin, and because it also included an internal spring biased in a direction to exert a backward pull on the puncture pin. This biasing was noted to sometimes snag and lodge on its way into the charged cartridge of conventional design during detonation--which interfered with the venting and inflation desired.
Thus, while some advances may have been made to determine if the cartridge is full or empty without first having to remove the cartridge from engagement, problems still remain to having these devices operate consistently, in providing the detection required.